1. Field of the Invention
The present invention relates to whip antennas mounted on vehicles such as automobiles, etc.
2. Prior Art
There are various structural types of antennas used as automobile radio antennas. Among these, one type of antenna which can be manufactured at low cost while still providing sufficient radio reception (which is a minimum requirement for such antennas) is a single-length whip antenna.
A single-length whip antenna usually includes a single, continuous rod-form conductive part which more or less matches a quarter wavelength of the FM wave band. When mounted on a vehicle, such antenna remains exposed on the outside of the vehicle body. Accordingly, high tensile materials having high recoil strength (such as high tensile strength stainless steel etc.) are used to form such an antenna so that the antenna will be able to withstand loads applied by obstructions during operation of the vehicle and/or when the vehicle is washed.
When the whip antenna is installed on a vehicle body in the assembly line, the antenna tends to occupy a relatively large space above the vehicle body. Thus, when vehicles having such an antenna installed thereon are transported, a great deal of space is wasted in order to accommodate the antenna. For this reason, the whip antennas are usually removable from the vehicle body (that is, from an attachment base which has been mounted to the vehicle body wall) via screws, etc. so as to save maximum amount of space and facilitate the transport of more vehicles.
Such antennas are, however, likely to suffer problems in that the material used to form the whip material must have a high tensile strength. However, such material is difficult to work with, and thus, it is difficult for example to cut threads thereon. As a result, it is also difficult to screw-couple such an antenna to the attachment base in an "as is" condition.
In view of these problems, a structure like that shown in FIG. 4 has been employed in the prior art. Specifically, a joint 2 is attached to the base end of a whip antenna element 1, and a male screw 3 connected to this joint 2 is screwed into a female screw 6 formed in a coupling element 5 of an attachment base 4. A material having a tensile strength lower than that of the whip antenna element 1 is used to form the joint 2 in order to secure good workability. At the same time, such material must be thoroughly sufficient in terms of strength. Accordingly, the manufacturing costs tend to be high.
In addition, there is another problem with prior art whip antennas in that even if a material of proven strength is used, the screw coupling must be in a restricted space. That is, the dimensions of the male screw portion cannot be very large. As a result, if the load (resulting from flexible bending of the whip antenna element 1) in the direction indicated by the arrow in FIG. 4 is concentrated in the screw area, the root portion of the male screw 3 may bend or break.